We are using a Seco Quadmo-747 E680 embedded Q7 board in our communications device. Most of our software is bound to the ubuntu 12.04 platform.
The hardware has been verified to work with windows 7 and IEMGD, using mostly standard configurations - including backlight control.
We are using the open source gma_500 driver, and modified the driver for to default to LVDS output and resolution to support our LCD. At present our only problem is that writing to the backlight registers(BLC_PWM_CTL/BLC_PWM_CTL2) only results in a hardly detectable glitch in the backlight - which is always on, and stays on. So we are definitely doing something wrong.
I do not have access to documentation regarding the backlight control in the tunnel creek platform. All I can find is some information on oak trail - perhaps the bitfields are different ?
Does anyone have any information that might help us along.
One issue is that the GMA_500 driver is actually for US15W (Poulsbo) and not E680 and the GMA tema never did a Linux driver for E680. The main 3d engine is the same, but there are differences in the display engine. Unfortunately, because of the 3d engine IP used in the E680, there is also restrictions on access to the internal owrkings, like the registers.
Two things come to mind:
1. Have you tried the EMGD Linux graphics driver as it might solve your issue? EMGD1.18 just released (is available currently on Intel Premier Support, but soon should be up here at http://www.intel.com/content/www/us/en/intelligent-systems/intel-embedded-media-and-graphics-driver/emgd-for-intel-atom-systems.html http://www.intel.com/content/www/us/en/intelligent-systems/intel-embedded-media-and-graphics-driver/emgd-for-intel-atom-systems.html
2. Have you looked into the PRM manuals that are published on the 01.org site for other chipsets as the E680 utilizes a newer display engine similar to some of those documented in the PRMs. (https://01.org/linuxgraphics/documentation https://01.org/linuxgraphics/documentation) or more specifically (https://01.org/linuxgraphics/sites/default/files/documentation/965_g35_vol_3_display_registers_updated.pdf https://01.org/linuxgraphics/sites/default/files/documentation/965_g35_vol_3_display_registers_updated.pdf)
Hope this helps.